From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BDED7C2D0E4 for ; Mon, 23 Nov 2020 14:05:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 53F7220888 for ; Mon, 23 Nov 2020 14:05:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="uc3VE1PZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730287AbgKWOFp (ORCPT ); Mon, 23 Nov 2020 09:05:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42408 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726508AbgKWOFo (ORCPT ); Mon, 23 Nov 2020 09:05:44 -0500 Received: from mail-yb1-xb43.google.com (mail-yb1-xb43.google.com [IPv6:2607:f8b0:4864:20::b43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16E30C061A4D; Mon, 23 Nov 2020 06:05:44 -0800 (PST) Received: by mail-yb1-xb43.google.com with SMTP id 2so15993082ybc.12; Mon, 23 Nov 2020 06:05:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=RhHqKgQbKUW77nc47JuvCnp+w8QNxENxQLSt6AHkTqQ=; b=uc3VE1PZNnY/Z1NgZXLeWe/Nj5hsoBfQkeeHXaE+d0SDr9xNRMPYxU1o6fpuaiqkgi yuFjhawxyOxFbziEfkWs4inb92LCIVTnNTVXAL7657JtY5jUPnHae9XC4JONvfltcDzK 9TpDS0ylXwfesoyru6or5tLuj2Wgq4fxc0XGG5evkxw7F5K63x1NbbMukm854FcfQLy0 gnTDe+NWIPcxyPxl6ZwlkcZY1OnasK1C98JFaIzSzrlrdcg6icgY2nCNokwGspTvBpMG u0c2fJxhgJsKPBZAzgP85ZG8VhKJUulmNcJ8sZ+phgCZ9U4trQ3IF/NnqsJiuQ1qY+5Q UH8Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=RhHqKgQbKUW77nc47JuvCnp+w8QNxENxQLSt6AHkTqQ=; b=qfu5ev+a4Mtxb/me5p98S+qpptw/liqOqi/Sn5haXVh4C3iZa/Rr1VO/RdFlRYFmI1 s2kn1wvg9ts9EsJlX8g3CJeCSRNYil+yfBHsTdyF3HJfbBmpnlalCpNeq2lfHeR6bkIC eKrnByi3tkSMwXRmTCDJWCc1yW3VnDwUIJOeshN6vpsXBmTvWv5hNWTaYLe/zmGvF4sR UJRQg5pa5sxtsrd+wg7QXtMX9UTOJiqN3Pl9j6wvDxpSpy1iq9oJ7ct126/9lGCJyaQB BqMp0EdLAQ2GVplt03VtpojSiDVmPVA2Hok29c4a+j/zowX4aTcB7WqHooUfgjGoJF5x jtRQ== X-Gm-Message-State: AOAM531VlvseIbNS+gH1i5feL/P9VJkSmr3dJPDYO1b4EwQ6YiYGVEFR 9sgGinzwDwKiV0L0AJnzQikU/rDGf2kYqM1cPuE= X-Google-Smtp-Source: ABdhPJz9DsZ58e7OIIOr/VE9Xtax3PWaLuFuRyVLpjTsCzIYcuPGWJiVUhGusztX9v02ET+47HU3GtURC6oS5LfC9Lw= X-Received: by 2002:a5b:40e:: with SMTP id m14mr35121900ybp.33.1606140343388; Mon, 23 Nov 2020 06:05:43 -0800 (PST) MIME-Version: 1.0 References: <20201120105344.4345c14e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <202011201129.B13FDB3C@keescook> <20201120115142.292999b2@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <202011220816.8B6591A@keescook> <9b57fd4914b46f38d54087d75e072d6e947cb56d.camel@HansenPartnership.com> In-Reply-To: From: Miguel Ojeda Date: Mon, 23 Nov 2020 15:05:31 +0100 Message-ID: Subject: Re: [PATCH 000/141] Fix fall-through warnings for Clang To: Finn Thain Cc: James Bottomley , Kees Cook , Jakub Kicinski , "Gustavo A. R. Silva" , linux-kernel , alsa-devel@alsa-project.org, amd-gfx@lists.freedesktop.org, bridge@lists.linux-foundation.org, ceph-devel@vger.kernel.org, cluster-devel@redhat.com, coreteam@netfilter.org, devel@driverdev.osuosl.org, dm-devel@redhat.com, drbd-dev@lists.linbit.com, dri-devel@lists.freedesktop.org, GR-everest-linux-l2@marvell.com, GR-Linux-NIC-Dev@marvell.com, intel-gfx@lists.freedesktop.org, intel-wired-lan@lists.osuosl.org, keyrings@vger.kernel.org, linux1394-devel@lists.sourceforge.net, linux-acpi@vger.kernel.org, linux-afs@lists.infradead.org, Linux ARM , linux-arm-msm@vger.kernel.org, linux-atm-general@lists.sourceforge.net, linux-block@vger.kernel.org, linux-can@vger.kernel.org, linux-cifs@vger.kernel.org, Linux Crypto Mailing List , linux-decnet-user@lists.sourceforge.net, Ext4 Developers List , linux-fbdev@vger.kernel.org, linux-geode@lists.infradead.org, linux-gpio@vger.kernel.org, linux-hams@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-i3c@lists.infradead.org, linux-ide@vger.kernel.org, linux-iio@vger.kernel.org, linux-input , linux-integrity@vger.kernel.org, linux-mediatek@lists.infradead.org, Linux Media Mailing List , linux-mmc@vger.kernel.org, Linux-MM , linux-mtd@lists.infradead.org, linux-nfs@vger.kernel.org, linux-rdma@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-scsi@vger.kernel.org, linux-sctp@vger.kernel.org, linux-security-module@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-usb@vger.kernel.org, linux-watchdog@vger.kernel.org, linux-wireless , Network Development , netfilter-devel@vger.kernel.org, nouveau@lists.freedesktop.org, op-tee@lists.trustedfirmware.org, oss-drivers@netronome.com, patches@opensource.cirrus.com, rds-devel@oss.oracle.com, reiserfs-devel@vger.kernel.org, samba-technical@lists.samba.org, selinux@vger.kernel.org, target-devel@vger.kernel.org, tipc-discussion@lists.sourceforge.net, usb-storage@lists.one-eyed-alien.net, virtualization@lists.linux-foundation.org, wcn36xx@lists.infradead.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , xen-devel@lists.xenproject.org, linux-hardening@vger.kernel.org, Nick Desaulniers , Nathan Chancellor , Miguel Ojeda , Joe Perches Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org On Sun, Nov 22, 2020 at 11:54 PM Finn Thain wrote: > > We should also take into account optimisim about future improvements in > tooling. Not sure what you mean here. There is no reliable way to guess what the intention was with a missing fallthrough, even if you parsed whitespace and indentation. > It is if you want to spin it that way. How is that a "spin"? It is a fact that we won't get *implicit* fallthrough mistakes anymore (in particular if we make it a hard error). > But what we inevitably get is changes like this: > > case 3: > this(); > + break; > case 4: > hmmm(); > > Why? Mainly to silence the compiler. Also because the patch author argued > successfully that they had found a theoretical bug, often in mature code. If someone changes control flow, that is on them. Every kernel developer knows what `break` does. > But is anyone keeping score of the regressions? If unreported bugs count, > what about unreported regressions? Introducing `fallthrough` does not change semantics. If you are really keen, you can always compare the objects because the generated code shouldn't change. Cheers, Miguel